简单模拟IOC容器：返回对象并能抛出异常

package com.zzj.annotation;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

//范围只限定类，存在周期运行后

@Target(ElementType.TYPE)

@Retention(RetentionPolicy.RUNTIME)

public @interface Component {

}

package com.zzj.vo;

public class Elephant {

}

package com.zzj.vo;

import com.zzj.annotation.Component;

@Component

public class Lion {

}

package com.zzj.vo;

import com.zzj.annotation.Component;

@Component

public class Tiger {

}

package com.zzj;

import java.io.File;

import java.util.HashMap;

import java.util.Map;

import org.springframework.beans.factory.NoSuchBeanDefinitionException;

import com.zzj.annotation.Component;

public class Application {

        //定义map集合存放对应类和对应的class对象

    private static Map<Class,Object> map = new HashMap<Class,Object>();

    static{

        String packageName = \"com.zzj.vo\";

        //获取包的绝对路径

        String path = ClassLoader.getSystemResource(\"\").getPath() + packageName.replace(\".\",File.separator);

        //路径中文转码,由于是静态方法不能使用

        //path = java.net.URLDecoder.decode(path,\"utf-8\");

        //采用字符替换

        path = path.replace(\"%e7%a8%8b%e5%ba%8f%e7%8c%bf\",\"程序猿\");

        //获取包里的所有类

        File[] files = new File(path).listFiles();

        //获取所有类的相对路径（包名+类名，无扩展名）

        for (File file : files){

            String fileName = file.getName();

            String className = packageName + \".\" + fileName.substring(0,fileName.indexOf(\".\"));

            //将获取的类放入Map集合，key为类型，value为映射对象(默认为对象地址)

            try {

                Class clazz = Class.forName(className);

                if(clazz.getAnnotation(Component.class) != null){

                    map.put(clazz,clazz.newInstance());

                }

            } catch (Exception e) {

                e.printStackTrace();

            }

        }

    }

        //抛出异常

        public static Object getBean(Class clazz){

        Object object =  map.get(clazz);

        if(object == null){

            throw new NoSuchBeanDefinitionException(\"No qualifying bean of type \'\"+clazz.getName()+\"\'available\");

        }

        return object;

    }

}
    

package com.zzj.exception;

public class NoSuchBeanDefinitionException extends RuntimeException{

    private static final long serialVersionUID = 8124869159299733396L;

    public NoSuchBeanDefinitionException(String msg) {

        super(msg);

    }

}

package com.zzj.test;

import com.zzj.vo.Lion;

import com.zzj.Application;

/*

 已知com.zzj.vo包下分别有Tiger、lion、Elephant三个Java源文件，请据此实现以下功能：

①、自定义一个名为Component的注解，要求该注解只能用于类且代码运行时该注解依然有效；

②、为Tiger和Lion类添加component注解

③、在Application类中定义静态代码块，该代码块可自动将有Component注解修饰的类创建对象并放在Map集合中；然后定义一个名为getBean的static方法，

要求传入Class类实例时返回该Class类对应类的对象，如果没有Class类对应的对象，则引发NoSuchBeanDefinitionException异常并

提示“No qualifying bean of type \'com.lq.vo.类名\'available”；

*/

public class Test {

    public static void main(String[] args){

        Object object = Application.getBean(Lion.class);

        System.out.println(object);

    }

}